A related application by the same inventor has been filed on even date herewith as U.S. Ser. No. (Docket No. EST 10200).
1. Field of the Invention
This invention relates to power transmissions for powered vehicles, such a automobiles and bicycles, and for machinery in general. In particular, the invention relates to a transmission in which input torque and speed may be varied continuously to provide a desired range of output torque and speed, and is not limited to any preselected gear ratios.
2. Description of Related Art
It is desirable to be able to vary an input to output shaft ratio smoothly and continuously over an infinite range of ratios as opposed to the discrete step change associated with gear changers. Prior art systems have attempted to replace discrete gears transmissions having fixed input/output ratios by various friction drive arrangements. Some of these systems have utilized rotatable conical surfaces to adjust input/output ratios. An early system is disclosed in U.S. Pat. No. 1,001,354 in which an adjustable belt was moved along the surface of rotatable cones to vary the output torque and speed, based on a given input. U.S. Pat. No. 3,793,910 discloses a complex, variable speed planetary drive system. The system includes a series of conical members in which movement is transmitted to ring and disk members which are positionable at various positions along the conical surface to change the speed ratio. U.S. Pat. No. 3,433,099 discloses a friction drive system having an adjustable axially split frusto-conical member. Another U.S. Pat. No. 5,020,384, utilizes various combinations of concave and/or convex surfaces to transmit torque across the friction boundaries of those surfaces. However, in all of them, at least one friction boundary in the chain of boundaries is required to slip while transmitting torque in order to effect a ratio change of input to output shafts. The force therefore to change the ratio relationship must be greater than the force of torque transmission. None of these systems utilize direct contact between all members which is adjustable in a slipless manner.
Other transmission systems are disclosed in U.S. Pat. Nos. 472,223, 1,425,172, 1,770,408, 2,209,497, 2,255,200, 2,359,540, 2,578,801, 4,098,145, 4,196,638, 4,428,246, 4,592,246, 4,850,235, 4,952,201, and 4,987,789. Disclosures in foreign patents include GB 281,942, DE 560,276 and DE 2,219,879.
Because of the excessive force required to slip moving, power transmitting surfaces across each other, traction and other drive transmission systems must be quite complex in order to provide continuous and infinite input/output ratios. A further problem with most continuously variable traction transmissions is the high level of complexity in the torque transmission paths and also in control actuation. A particular problem with those traction transmissions that utilize multiple torque paths is that, in the process of varying the input/output ratio, all paths must be absolutely identical in size, otherwise one path will try to cause a greater output than the other parts and slippage will be induced, the torque for which must come from the prime power source through the non-slipping path. There is nothing in these prior art systems which transmits torque across a friction boundary in a slipless and stepless manner in response to a simple linear control motion. Further, prior art transmissions generally require a separate input to change the input/out ratio.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a traction transmission for continuously and infinitely varying input/output ratios of torque and speed.
It is another object of the present invention to provide a transmission for continuously varying the rotational relationship between an input shaft and an output shaft of a traction transmission by simple low force motion of a control element of the transmission which may be actuated internally or externally to the transmission.
A further object of the invention is to provide a transmission in which the rotational relationship of the members is rapidly actuatable throughout the entire range simultaneously with the transmission of the full torque permitted by the friction interfaces.
It is yet another object of the present invention to provide a transmission in which the input/output ratio is automatically changed by the transmission as a function of required output torque.
It is yet a further object of the present invention to provide a transmission in which the input/output ratio is automatically changed by the transmission as a function of required output torque, and whereby this torque function is adjustable externally to the transmission.
It is another object of the present invention to provide a transmission in which the input/output ratio may be changed manually external to the transmission.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.